A freestanding fuel rack includes an array of vertical storage cavities used to store nuclear fuel in an upright configuration. Each storage cavity generally provides a square prismatic opening to store one spent nuclear or fresh (unburned) fuel. The cross section of the openings is slightly larger than that of the fuel assembly to facilitate the latter's insertion or withdrawal. From the structural standpoint, the fuel rack is a cellular structure supported on a number of pedestals that transfer the dead load of the rack and its stored fuel to the pool's slab. It is preferable to install the racks in a freestanding configuration to minimize cost and dose (if the pool is populated with irradiated fuel).
The rack modules in a fuel pool typically have the appearance of a set of rectangular cavities arranged in a rectilinear array. The racks are typically separated by small gaps. Freestanding racks, however, are liable to slide or rotate during seismic event. If the plant's design basis is moderate then the kinematic movement of the racks may not be enough to cause inter-rack collisions or rack-to-wall impacts. However, if the seismic event is strong then the response of the racks may be too severe (e.g., large displacements, significant rack impact forces, etc.) to be acceptable. Reducing the kinematic response of the racks under strong seismic events (e.g., earthquakes) while preserving their freestanding disposition is therefore desirable.